The proposed studies will examine the properties of the Na+-Ca++ exchange transport system found in plasmalemma from mammalian brain. 1. We will examine the ability of structural analogues of amiloride to inhibit Na+ Ca++ exchange in membrane visicles. The goal of these studies is to characterize the drug binding site, develop a more potent inhibitor of Na+ Ca++ exchange, find a photo affinity label for the carrier, and examine the asymmetry of the carrier. 2. We will fractionate and purify the Na+ Ca++ carrier. During purification, the carrier will be assayed by reconstitution and transport or by drug (amiloride-like compounds) interaction. The long-term aim is to study the molecular properties of the carrier and to examine the transport properties of the carrier in the absence of other ion channels and carriers. 3. The transport properties of the fractionated and/or purified carrier reconstituted in membrane vesicles will be examined. We will measure the flux ratio (Na+:Ca++) of the carrier, determine whether the carrier is electrogenic, examine the relationship of Ca++ Ca++ exchange to Na+ Ca++ exchange, and determine what factors (i.e., ATP, membrane potential, Li+, intra- versus extravesicular Na+) regulate the carrier. The aim of these studies is to determine under what conditions the carrier functions in whole cells. Regulation of cell Ca2+ (by Na+ Ca++ exchange) may be important in digitalis-induced positive ionotropy, vasoconstruction in hypertension, epilepsy, and may play a pivotal role in ischemia-induced cell death. Amiloride-like drugs, which alter Ca++ transport may be important in preventing cerebral damage from ischemia or other insult.